In addition to being a great stand-alone side, these slow-cooker mushrooms are also excellent tossed in a salad or stir-fry. Be sure to buy whole cremini mushrooms so they will retain their texture and not turn mushy during the long cook time. If you don't want to wait for the mushroom mixture to concentrate during the 1 hour and 30 minutes of cooking it uncovered, then cook it, uncovered, just long enough for the mushrooms to brown. Then drain the liquid and bring it to a boil in a saucepan. Once the liquid has thickened, stir in the mushrooms and vinegar and sprinkle with the scallions.